Integrated circuits and discrete semiconductor devices, such as transistors, are fabricated on substrate wafers. During fabrication and subsequent handling, wafers are loaded in a cassette, which the semiconductor fabrication and handling equipment is adapted to receive. Cassettes typically contain from 1 to 26 wafers and can weigh more than 10 pounds. The wafers are of standard sizes, typically from about six inches to about twelve inches in diameter. The wafers are positioned within the cassette in parallel slots or grooves on opposing sides of a standard cassette and are loaded and unloaded through an opening at the top portion of the cassette. When the wafers are vertically oriented the cassette is said to be vertically oriented; when the wafers are horizontally oriented, the cassette is said to be horizontally oriented.
The cassette typically must be positioned vertically for safe wafer handling by human operators or robotic handling devices between work stations in the semiconductor fabrication process. However, the cassette typically must generally be oriented horizontally for access by work station robotic arms. Thus, the cassette must be rotated or pivoted between the vertical and horizontal positions. The majority of semiconductor equipment requires the human operator to manually rotate the cassette.
Manual rotation of wafer-loaded cassettes has led to long-term disabilities resulting from repetitive stress syndrome. Safety guidelines for Ergonomic/Human Factors Engineering of Semiconductor Manufacturing Equipment, SEMI S8-95, Article 11, require that human operators avoid simultaneously lifting and rotating or manually orienting products and/or containers. Accordingly, there is a need for automated wafer cassette rotation devices.
Previous approaches to automating wafer cassette rotation typically involve devices that are both large and complex. The large size of the prior cassette rotation devices is undesirable as they require more room in clean room areas of limited space. The large size of the devices also limits retrofitting of cassette rotation devices into existing fabrication processes or work stations, as the processing equipment, like most clean rooms, offers only limited available space. Further, the complexity of the prior devices has created loss of productivity due to frequent mechanical failures, increased contamination of wafers, and require extensive downtime for maintenance.